The drugs at the core of the mystery — popularized as "The French Connection" in a 1969 book by Robin Moore and an Academy Award-winning film that followed two years later — were secreted in compartments in a 1960 Buick loaded aboard the liner United States sailing from Le Havre, France, to New York. The car and its 112 pounds of heroin were later claimed by a Lucchese family underling, Patsy Fuca, who, as it happened, was being tailed by a pair of dogged New York narcotics detectives, Eddie Egan and Sonny Grosso.

The drug bust in January 1962 was widely hailed as a record. But the heroics proved short-lived. In six thefts between March 1969 and January 1972, someone signing the register as Detective Joseph Nunziata, a member of the narcotics bureau's widely corrupt special investigations unit, and using fictitious badge numbers, removed the French Connection drugs along with another 300 pounds of heroin and cocaine from the police property vault at 400 Broome Street (now a New York University dorm).

Handwriting analysis and a discovered fingerprint never established that Detective Nunziata actually signed the police register. But eight months before the thefts were discovered, Detective Nunziata, charged with corruption in an unrelated case, was found shot to death in his car. It was ruled a suicide.

Among the suspects were: drug kingpin Vincent Papa; Frank King, a retired narcotics detective and private eye working for Papa; Pat Intrieri who, upon his retirement from the force, joined King as a bodyguard for one of Papa's sons; and Vincent Albano, a former narcotics detective who had served under Intrieri and had survived a murder attempt in 1969, only to be slain in 1985:

Thomas P. Puccio, then a Brooklyn federal prosecutor, focused on Mr. King and Mr. Intrieri, but failed to tie them to the drug thefts. Mr. Puccio charged them instead with tax evasion for unexplained income, winning convictions and five-year sentences for both, along with three years for tax evasion by Mr. Albano. But the case remained a puzzle, Mr. Puccio conceded in an interview. "We never really conclusively solved it," he said.

Intrieri insists that he had nothing to do with the drug heist, and is hoping that the mobster can help clear his name after reading a 2008 biography by Philip Carlo on Casso:

Still indignant over his conviction more than 30 years later, Mr. Intrieri — who held 15 police citations for bravery and valor — saw in Mr. Carlo's book that Mr. Casso had named Mr. Albano and a mob associate as two of the French Connection thieves. The book related how Mr. Albano had been shot to death in Brooklyn in 1985, and how Mr. Casso had supplied the gun and helped dump the body on Staten Island. Mr. Carlo, in an interview, said Mr. Casso had told him Mr. Albano had conceived the drug heist and asked Mr. Casso how to carry it out. Mr. Intrieri, in his own manuscript, "The French Connection: The Aftermath," told of running into Mr. Albano several times over the years — including in 1980 while Mr. Albano was casing a Queens bank — and said that Mr. Albano had laughed at hearing that Mr. Intrieri was a suspect in the drug thefts.

Casso, serving multiple life sentences after pleading guilty to 15 murders and tied to 22 other murders, is now offering to cooperate in solving the drug thefts from the NYPD property vault in exchange for some relief from prison although prosecutors appear cautious about any deal:

[Casso has] been accused of plotting to kill a federal judge and prosecutors, and violating the terms of his agreement to turn informant as one of the highest-level mobsters ever to flip — becoming the only major Mafia defector to be thrown out of the federal witness protection program. Mr. Casso has also waffled on whether he corrupted an F.B.I. agent and hired two New York City police detectives, Louis J. Eppolito and Stephen Caracappa, as mob assassins. * * * If, moreover, he still wonders why the authorities are leery of his offers, Mr. Casso may have provided the answer to his biographer, Philip Carlo. In his 2008 book, "Gaspipe: Confessions of a Mafia Boss," Mr. Carlo, a longtime friend of the Casso family, outlined several of the mobster’s escape schemes, including the planned ambush of a van carrying him back from court after his capture New Jersey in 1993. "He's where he should be," said Gregory O'Connell, a former federal prosecutor in Brooklyn who initially interviewed Mr. Casso with his late partner, Charles Rose, and called him "the most treacherous sociopath we ever dealt with."

In addition to offering up details on the NYPD drug theft, Casso also claims to have the scoop on other mob crimes:

Mr. Casso offered details of the 1986 car bombing aimed at John Gotti that killed his Gambino family underboss, Frank DeCicco; the killing of a Russian mob associate, Michael Markowitz, in 1989; and the apparently unreported killing of a Jewish drug importer near Mr. Albano's office around 1980.

This Tuesday Michael F. Vecchione, chief of the rackets division in the Brooklyn district attorney's office, will visit Casso at the Federal Medical Center in Butner, N.C. to hear out the mobster.